500 error when adding a Service with an empty "url" value

[subnetmarco]

Executing http :8001/services name=test url= triggers:

lua coroutine: runtime error: /usr/local/share/lua/5.1/kong/api/api_helpers.lua:81: attempt to index local 'parsed_url' (a nil value)
stack traceback:
coroutine 0:
	/usr/local/share/lua/5.1/kong/api/api_helpers.lua: in function 'resolve_url_params'
	/usr/local/share/lua/5.1/kong/api/routes/services.lua:17: in function </usr/local/share/lua/5.1/kong/api/routes/services.lua:16>
coroutine 1:
	[C]: in function 'resume'
	/usr/local/share/lua/5.1/lapis/application.lua:393: in function 'handler'
	/usr/local/share/lua/5.1/lapis/application.lua:130: in function 'resolve'
	/usr/local/share/lua/5.1/lapis/application.lua:161: in function </usr/local/share/lua/5.1/lapis/application.lua:159>
	[C]: in function 'xpcall'
	/usr/local/share/lua/5.1/lapis/application.lua:159: in function 'dispatch'
	/usr/local/share/lua/5.1/lapis/nginx.lua:215: in function 'serve_admin_api'
	content_by_lua(nginx-kong.conf:281):2: in function <content_by_lua(nginx-kong.conf:281):1>, client: 172.18.0.1, server: kong_admin, request: "POST /services HTTP/1.1", host: "localhost:8001"
2018/05/10 07:49:03 [error] 116#0: *38976 [lua] init.lua:135: handle_error(): /usr/local/share/lua/5.1/lapis/application.lua:397: /usr/local/share/lua/5.1/kong/api/api_helpers.lua:81: attempt to index local 'parsed_url' (a nil value)
stack traceback:
	/usr/local/share/lua/5.1/kong/api/api_helpers.lua: in function 'resolve_url_params'
	/usr/local/share/lua/5.1/kong/api/routes/services.lua:17: in function </usr/local/share/lua/5.1/kong/api/routes/services.lua:16>

stack traceback:
	[C]: in function 'error'
	/usr/local/share/lua/5.1/lapis/application.lua:397: in function 'handler'
	/usr/local/share/lua/5.1/lapis/application.lua:130: in function 'resolve'
	/usr/local/share/lua/5.1/lapis/application.lua:161: in function </usr/local/share/lua/5.1/lapis/application.lua:159>
	[C]: in function 'xpcall'
	/usr/local/share/lua/5.1/lapis/application.lua:159: in function 'dispatch'
	/usr/local/share/lua/5.1/lapis/nginx.lua:215: in function 'serve_admin_api'
	content_by_lua(nginx-kong.conf:281):2: in function <content_by_lua(nginx-kong.conf:281):1>, client: 172.18.0.1, server: kong_admin, request: "POST /services HTTP/1.1", host: "localhost:8001"

[thibaultcha]

Fixed with #3452 merged. Thanks @bungle! This issue was also spotted in EE in the internal proxies code paths but caught during a review, so we should be safe now.